1. Field of the Invention
The invention relates to a machining center for the machining (drilling, milling, etc.) of one or more parts clamped to a fixture; and, more particularly, to an integral continuous pressure hydraulic pressure clamping system for use with the machining center to supply hydraulic fluid to the fixtures to provide a controllable clamping force.
2. Related Art
Machining centers, such as CNC machining centers, are widely used in the production of precision parts. Generally, most machining centers employ a pallet changing station. The unmachined parts are clamped to a fixture that is moved into and out of the machining area by the pallet changing station.
The pallet changing station typically comprises an external housing in which is mounted a vertically-oriented rotating column that carries a dividing wall and a platform on which the fixtures are positioned. The dividing wall effectively encloses a portion of the column and divides the interior of the pallet changing station into a load area and a machining area. Each of the load area and the machining area support a fixture. In that manner, the parts of the fixture in the machining area can be machined while the fixture in the load area can be loaded with new parts or the fixture replaced entirely. The fixture in the load area can be rotated for better access in the load area.
To exchange one fixture for another the machining area fixture is retracted onto the rotating platform of the pallet changing station. The column is moved upward and rotated to move the one fixture currently in the machining area to the loading area, which simultaneously moves the fixture that was in the loading area into the machining area. Typically, the rotational movement of the column is coupled with a vertical upward movement, which unseals the dividing wall carried by the column with respect to the external housing. The rotation is typically limited to approximately 180xc2x0 in a clockwise/counterclockwise operation.
The supplying of hydraulic fluid to the fixtures is a continuous source of problems because the fluid lines extending to the fixtures must be capable of rotating with the column of the pallet changing station while accommodating the extension and retraction and rotation of the fixture relative to the column without tangling or breaking the hydraulic connection or requiring their uncoupling and recoupling.
Applicants previous solution to addressing the problems of supplying hydraulic lines to the fixtures included directing the hydraulic lines into the pallet changing station along the rotating column and delivering the hydraulic lines from the rotating column to the fixture through a multi-segmented articulating arm. One end of each arm is mounted to an opposing portion of the rotating shaft and the other end of the arm mounts to a rotary coupling adapted to mount to the fixture. A disadvantage of this system is that the hydraulic lines required individual rotary couplings to permit them to run along the rotating column without twisting during rotation of the column and still be fed through the articulating arms. The repeated rotation of the pallet changing station loosened the individual rotary couplings requiring frequent maintenance and lost production time.
The invention relates to an improved machining center for machining parts carried by a fixture. The machining center comprises a housing that defines the fixture loading area for receiving the fixture and the machining area for receiving the fixture during the machining of the parts. A machining tool is located in the machining area for performing machining operations on a part that is carried by the fixture. The machining center further comprises a pallet changing station having a vertically-oriented rotating column assembly and a platform for supporting the fixture. The platform is mounted to the column and has a first portion that is located in the loading area and a second portion located in the machining area. The rotation of the column assembly moves the platform first portion from the loading area to the machining area and the platform second portion from the machining area to the loading area. In this manner, the fixture is moved on the loading area to the machining area for performing the machining operations on the parts and from the machining area to the loading area for removing the machined parts from the fixture. A clamping system comprising a hydraulic conduit extending into the pallet changing station is provided for supplying pressurized hydraulic fluid to the fixture from a source of pressurized hydraulic load to aid in the clamping of the parts to the fixture. The improvement in the machining center comprises the column assembly having a portion with an internal bore forming part of the hydraulic conduit for fluid connection of hydraulic fluid source with the clamping system.
Preferably, the internal bore has an inlet located on an exterior portion of the column assembly for fluidly connecting with the hydraulic fluid source and an outlet on an exterior portion of the column assembly for fluidly connecting with the clamping system. The outlet can be located interiorly of the housing and within the pallet changing station. The outlet can be located exteriorly of the housing.
The machining center can further comprise a rotary coupling for fluidly connecting the inlet of the internal bore with the hydraulic fluid source. A second rotary coupling can be provided for connecting the hydraulic conduit with the fixture. Preferably, the hydraulic conduit comprises a hydraulic line extending from the bore outlet to the fixture.
The machining center can include an articulating arm with a hollow interior. The arm includes a first end that is mounted to the column assembly and a second end that mounts to the second rotary coupling. The hydraulic line extends through the hollow interior of the arm from the column assembly to the second rotary coupling. The arm preferably comprises multiple segments, with each of the segments being hingedly connected to prevent their relative rotation. The hinged connections are oriented to permit the arm to rotate relative to both a horizontal aid a vertical axis.
The column assembly preferably comprises a shaft with an internal bore forming a portion of the column assembly that forms part of the hydraulic conduit and a column to which the platform is mounted. A lower end of the shaft is mounted to an upper end of the column to form the column assembly. The shaft comprises a base forming the shaft lower end, and the base has a peripheral wall on which the outlet is located. The shaft also has an upper on which the inlet is located. The bore comprises a first portion that extends from the inlet axially through the shaft toward the base and a second portion that extends radially from the first portion through the base to the outlet.
Preferably, there are multiple hydraulic conduits and multiple bores with corresponding inlets located on the shaft upper end and corresponding outlets located on the base peripheral wall. The bores are preferably formed by gun-drilling.
The machining center can further comprise a lift mechanism that is mounted to the housing and operably coupled to the shaft to thereby move the shaft between a lowered position and a raised position to effect the raising and lowering of the platform. The lift mechanism includes a lift cylinder having a hollow interior that slidably receives the shaft and a piston fixedly mounted to the shaft and located within the lift cylinder hollow interior. Pressurized fluid is introduced and exhausted from the lift cylinder to reciprocate the piston within the lift cylinder to move the shaft between the lowered and raised positions.
In another aspect, the invention relates to a column assembly for a machining center for machining parts carried by a fixture. The machining center comprises a housing defining a fixture loading area for receiving the fixture and a machining area for receiving the fixture during the machining of parts. A machining tool is located in the machining area for performing machining operations on a part carried by the fixture. The machining center further comprises a pallet changing station having a movable platform with a first portion located in the loading area and a second portion located in the machining area. The movement of the platform moves the platform first portion from the loading area to the machining area and the platform second portion from the machining area to the loading area to thereby move the fixture between the loading area and the machining area. A clamping system is provided and comprises a hydraulic conduit extending into the pallet changing station for supplying pressurized hydraulic fluid to the fixture from a source of pressurized hydraulic fluid to aid in the clamping of the parts to the fixture. The column assembly comprises a portion having an internal bore that forms part of the hydraulic conduit and is mounted for rotational movement relative to the housing. The column assembly carries the platform whereby the rotation of the column assembly moves the platform first portion from the loading area to the machining area in the platform second portion from the machining area to the loading area.